1. Technical Field of the Invention
The present invention relates generally to a method of cutting slots in a hard material, and more particularly to an improved method of machining slots and material feed holes in a die for molding a honeycomb structure, for example.
2. Background of Related Art
U.S. Pat. No. 4,640,454 to Yamamoto et al. teaches an extrusion die for making honeycomb structures of ceramics used as a catalyst carrier of a catalytic converter for automotive vehicles.
Such honeycomb structures have thin honeycomb walls of the order of 100 xcexcm. The extrusion die, thus, needs to have formed therein slots whose width is of the order of 105 to 110 xcexcm and material feed holes communicating with the slots. Usually, the slots are cut using a disc-shaped rotary cutter having a thickness of 100 xcexcm, and the material feed holes are drilled.
The conventional die machining techniques, however, have encountered the drawbacks in that the drilling of the material feed holes causes burrs to occur at portions of the holes communicating with the slots, thereby resulting in defects in the honeycomb structures and in that the cutter is deformed or shifted out of a preselected cutting path during cutting of each slot because of thinness thereof, thereby resulting in the curved slots.
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is another object of the present invention to provide an improved method of machining straight slots and holes communicating with the slots in a die without any defects.
According to one aspect of the present invention, there is provided a method of making a molding die comprising the steps of: (a) preparing a die material having a slot-forming surface and a molding material feed hole-forming surface opposite the slot-forming surface; (b) machining a slot in the slot-forming surface of the die material; (c) machining a shallow hole in the shallow hole-forming surface of the die material, the molding material feed hole having a depth shorter than a molding material feed hole; and (d) forming the molding material feed hole by subjecting a bottom of the shallow hole to non-contact machining to establish physical communication between the slot and the shallow hole.
In the preferred mode of the invention, the non-contact machining is one of electrochemical machining, electric discharge machining, and laser beam machining.
The shallow hole is 0.05 to 2.0 mm shorter in depth than the molding material feed hole.
The molding die is designed to make a honeycomb structure.
According to the second aspect of the invention, there is provided a method of making a molding die comprising the steps of: (a) preparing a die material having a slot-forming surface and a molding material feed hole-forming surface opposite the slot-forming surface; (b) machining a molding material feed hole in the molding material feed hole-forming surface of the die material; (c) mounting the die material on a work table of a grooving machine with the molding material feed hole-forming surface exposed to a vacuum chamber provided in the work table; and (d) machining a slot, which communicates with the molding material feed hole, in the slot-forming surface of the die material using a rotary disc-shaped cutter having a thickness of 150 xcexcm or less while decreasing an internal pressure of the vacuum chamber of the grooving machine.
In the preferred mode of the invention, the molding die is designed to make a honeycomb structure.
According to the third aspect of the invention, there is provided a method of making a molding die comprising the steps of: (a) preparing a die material having a slot-forming surface and a molding material feed hole-forming surface opposite the slot-forming surface; (b) machining molding material feed holes in the molding material feed hole-forming surface of the die material; (c) mounting the die material on a work table of a grooving machine with the molding material feed hole-forming surface exposed to a vacuum chamber provided in the work table; and (d) machining slots, which communicate with the molding material feed holed, in the slot-forming surface of the die material using a rotary disc-shaped cutter having a thickness of 150 xcexcm or less while decreasing an internal pressure of the vacuum chamber of the grooving machine, the machining step including a masking step of masking at least part of the slots which have already been machined during machining the slots.
In the preferred mode of the invention, the molding die is designed to make a honeycomb structure.
According to the fourth aspect of the invention, there is provided a method of making a molding die comprising the steps of: (a) preparing a die material, the die material having a slot-forming surface and a molding material feed hole-forming surface opposite the slot-forming surface, the slot-forming surface having formed on an end thereof a tapered portion; (b) machining a molding material feed hole in the molding material feed hole-forming surface of the die material; and (c) machining a slot, which communicates with the molding material feed hole, in the slot-forming surface of the die material toward the tapered portion using a disc-shaped cutter having a thickness of 150 xcexcm or less so that the cutter may leave the tapered portion at completion of machining the slot.
In the preferred mode of the invention, the tapered portion of the slot-forming surface of the die material is so formed that the thickness of the tapered portion is continuously decreased.
The tapered portion of the slot-forming surface is inclined at an angle of 18xc2x0 or less to a reference surface extending in parallel to the slot.
The tapered portion may alternatively be curved.
The tapered portion of the slot-forming surface of the die material may alternatively be so formed that the thickness of the tapered portion is decreased stepwise.
The molding die is designed to make a honeycomb structure.
According to the fifth aspect of the invention, there is provided a method of making a molding die comprising the steps of: (a) preparing a die material having a slot-forming surface and a molding material feed hole-forming surface opposite the slot-forming surface; (b) machining molding material feed holes in the molding material feed hole-forming surface of the die material; and (c) machining slots which communicate with the molding material feed holes in the slot-forming surface of the die material in sequence at regular pitches using a rotary cutter having a thickness 150 xcexcm or less, each of the slots being formed at an interval two times the regular pitch or more away from immediately preceding one of the slots.
In the preferred mode of the invention, the interval is 2.0 mm or more.
Each of the slot is cut close to a line which divides an machined portion of the slot-forming surface into two equal parts.
A step is further provided which monitors the breakage of the rotary cutter during machining of the slots to determine whether the cutter has reached a service life thereof or not.
The cutter damage monitoring step determines the number of breakages, the depth of each breakage, and the width of each breakage and compares them with reference values in determining whether the cutter has reached the service life or not.
The reference values of the number of breakage, the depth of each breakage, and the width of each breakage is 1, 0.5 mm, and 0.5 mm, respectively.
The molding die is designed to make a honeycomb structure.